PTFE and other fluoropolymers are most commonly commercially produced by emulsion polymerization. Emulsion polymerization provides a better balance of economy, quality, environmental friendliness, and minimal health risks. However, it is believed that commercially suitable emulsion polymerization processes for making fluoropolymers require a fluorinated emulsifier, such as PFOA and/or a salt of PFOA.
Until fairly recently, it was believed that PFOA and its salts were the only suitable emulsifiers that could be used to achieve acceptable yields and product quality during emulsion polymerization of fluorinated monomers to produce PTFE and other fluoropolymers. However, it has been reported that PFOA and its salts are very persistent in the environment, and have been found in the blood of the general population of the United States. It has also been found that PFOA and its salts cause developmental and other adverse affects in laboratory animals. It is believed that PTFE products and other fluoropolymer products may contain trace amounts of PFOA and/or other related perfluoronated chemicals as impurities.
Because of the environmental concerns and potential health risks associated with the use of PFOA and/or its salts, in 2006 the United States Environmental Protection Agency and eight major manufacturers of fluoropolymers launched the 2010/15 PFOA Stewardship Program, in which the manufacturers have committed to reduce facility emissions and product content of PFOA and related chemicals by 95% by 2010, and to work toward eliminating emissions and product content by 2015.
Examples of new emulsion polymerization processes for making fluoropolymers using reduced amounts of PFOA and/or its salts are described in the literature. U.S. Pat. No. 7,851,573 to Higuchi et al. describes an aqueous emulsion polymerization process which employs a polyfluoroethylene oxide carboxylate as a substitute for PFOA. The entire content of U.S. Pat. No. 7,851,573 is hereby incorporated by reference herein. U.S. Pat. No. 7,834,137 to Higuchi et al. describes a process for producing an aqueous fluorinated polymer dispersion having a reduced content of a fluorinated emulsifier by using a weakly basic anion-exchange resin to absorb and remove the fluorinated emulsifier from the emulsion with excellent efficiency. The entire contents of U.S. Pat. No. 7,834,137 is hereby incorporated by reference herein. U.S. Pat. No. 7,838,608 to Hintzer et al. describes an aqueous emulsion polymerization of PTFE employing a fluorinated aliphatic carboxlate surfactant that has at least one carbon atom in the aliphatic group that is not fully fluorinated as a substitute for PFOA and/or its salts.
Dyneon, a 3M Company, has announced its Dyneon ADONA™ emulsifier that is said to completely eliminate the use of ammonium perfluorooctanate (APFO), a salt derived from PFOA, from its fluoropolymer production processes. It has been stated that ADONA™ emulsifier is 10 to 30 times less toxic than APFO in developmental toxicity studies in rodents, and 5 to 17 times less toxic than APFO in 28-day oral toxicity studies in rats.
Perfluorobutanic acid (PFBA) and/or its salts have been proposed as a substitute for PFOA and/or its salts as an emulsifier for polymerization of fluoropolymers.
The approaches that have been explored for reducing or eliminating the use of PFOA and/or its salts have generally focused on either substituting a less toxic fluorinated emulsifier or facilitating removal of the emulsifier from the polymer dispersion after polymerization is completed.